Structure 3.2.7
Stereoisomers
Molecules with the same connectivity but different spatial arrangement.
A. Cis-Trans (Geometric) Isomerism
Can occur in alkenes or cyclic compounds.
Conditions
- Restricted Rotation: Due to bond (alkene) or ring structure.
- Distinct Groups: Each carbon of the double bond/ring must have two different groups attached.
Forms
- Cis (Z): High priority groups on the same side.
- Trans (E): High priority groups on opposite sides.
B. Optical Isomerism (Chirality)
The Chiral Center
A Carbon atom bonded to 4 different groups.
Key Properties
- Enantiomers: Describe the two isomers. They are non-superimposable mirror images (like left and right hands).
- Optical Activity: Enantiomers rotate plane-polarized light in equal but opposite directions (+/-).
- Racemic Mixture: A 50:50 mixture of both enantiomers. It is optically inactive because the rotations cancel out.